4,005 research outputs found
Concepts, Design and Implementation of the ATLAS New Tracking (NEWT)
The track reconstruction of modern high energy physics experiments is a very complex task that puts stringent requirements onto the software realisation. The ATLAS track reconstruction software has been in the past dominated by a collection of individual packages, each of which incorporating a different intrinsic event data model, different data flow sequences and calibration data. Invoked by the Final Report of the Reconstruction Task Force, the ATLAS track reconstruction has undergone a major design revolution to ensure maintainability during the long lifetime of the ATLAS experiment and the flexibility needed for the startup phase. The entire software chain has been re-organised in modular components and a common Event Data Model has been deployed during the last three years. A complete new track reconstruction that concentrates on common tools aimed to be used by both ATLAS tracking devices, the Inner Detector and the Muon System, has been established. It has been already used during many large scale tests with data from Monte Carlo simulation and from detector commissioning projects such as the combined test beam 2004 and cosmic ray events. This document concentrates on the technical and conceptual details of the newly developed track reconstruction, also known as New Tracking
QCD corrections to the forward-backward asymmetries of and quarks at the Z pole
Measurements of the forward-backward production asymmetry of heavy quarks in Z decays provide a precise determination of \swsqeffl . The asymmetries are sensitive to QCD effects, in particular hard gluon radiation. In this paper QCD corrections for \AFBbb~ and \AFBcc~ are discussed. The interplay between the experimental techniques used to measure the asymmetries and the QCD effects is investigated using simulated events. A procedure to estimate the correction needed for experimental measurements is proposed, and some specific examples are given
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ATLAS Tracking Event Data Model
In this report the event data model (EDM) relevant for tracking in the ATLAS experiment is presented. The core component of the tracking EDM is a common track object which is suited to describe tracks in the innermost tracking sub-detectors and in the muon detectors in offline as well as online reconstruction. The design of the EDM was driven by a demand for modularity and extensibility while taking into account the different requirements of the clients. The structure of the track object and the representation of the tracking-relevant information are described in detail
The Algorithm Steering and Trigger Decision mechanism of the ATLAS High Level Trigger
Given the extremely high output rate foreseen at LHC and the general-purpose
nature of ATLAS experiment, an efficient and flexible way to select events in
the High Level Trigger is needed. An extremely flexible solution is proposed
that allows for early rejection of unwanted events and an easily configurable
way to choose algorithms and to specify the criteria for trigger decisions. It
is implemented in the standard ATLAS object-oriented software framework,
Athena. The early rejection is achieved by breaking the decision process down
into sequential steps. The configuration of each step defines sequences of
algorithms which should be used to process the data, and 'trigger menus' that
define which physics signatures must be satisfied to continue on to the next
step, and ultimately to accept the event. A navigation system has been built on
top of the standard Athena transient store (StoreGate) to link the event data
together in a tree-like structure. This is fundamental to the seeding
mechanism, by which data from one step is presented to the next. The design
makes it straightforward to utilize existing off-line reconstruction data
classes and algorithms when they are suitableComment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 8 pages, PDF, PSN TUGT00
Refitting of combined inner detector and muon spectrometer tracks from Monte Carlo samples by using the Kalman fitter and the STEP algorithm in the ATLAS experiment
In this paper we refit combined muon tracks using the Kalman fitter and the simultaneous track and error propagation (STEP) algorithm of the ATLAS tracking software. The muon tracks are simulated by GEANT4 in the full detector description, reconstructed by MUID, and refitted by the Kalman fitter in the ATLAS TrackingGeometry. The relative transverse momentum resolution of the refitted tracks is compared to the resolution of the refits done by the global chi-square track fitter, along with the resolution found by the MUID and STACO muon combination algorithms. Reconstructed invariant masses are compared in a similar way
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ATLAS Inner Detector Event Data Model
The data model for event reconstruction (EDM) in the Inner Detector of the ATLAS experiment is presented. Different data classes represent evolving stages in the reconstruction data flow, and specific derived classes exist for the sub-detectors. The Inner Detector EDM also extends the data model for common tracking in ATLAS and is integrated into the modular design of the ATLAS high-level trigger and off-line software
ATLAS Detector Paper Back-Up Note: Electrons and Photons
This is the supporting note to the ATLAS Detector paper for electron and photon reconstruction with the Inner Detector. It describes the software used to produce the results presented in the ATLAS Detector paper
The ATLAS Data Quality Defect Database System
The ATLAS experiment at the Large Hadron Collider has implemented a new
system for recording information on detector status and data quality, and for
transmitting this information to users performing physics analysis. This system
revolves around the concept of "defects," which are well-defined, fine-grained,
unambiguous occurrences affecting the quality of recorded data. The motivation,
implementation, and operation of this system is described.Comment: 6 pages, 3 figures, published in EPJ C. (v2: as published
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations
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